Simultaneous determination of lead and cadmium in water by metal oxide framework complex-modified glassy carbon electrodes

Abstract

Lead (Pb) and cadmium (Cd) are pervasive environmental pollutants known for their significant biological toxicity. The traditional methods for detecting these ions often necessitate large-scale instruments and complex procedures. In contrast, electrochemical detection methods offer advantages such as rapidity, portability, and sensitivity, making them suitable for the simultaneous detection of heavy metals. Metal-organic frameworks (MOFs), characterized by their exceptional adsorption and enrichment capabilities for heavy metal ions, have shown promise in this regard. Nevertheless, the poor conductivity of most MOFs has limited their electrochemical applications. In this study, glassy carbon electrodes (GCEs) were modified using the MOF ZIF-8, in combination with a bismuth complex and carboxylated multi-walled carbon nanotubes, resulting in the fabrication of Bi@ZIF-8/CMWCNTs/GCE electrochemical sensors. Leveraging the porous nature and large specific surface area of ZIF-8, the lead and cadmium ion adsorption by bismuth akin to mercury, and the conductivity of carboxylated multi-walled carbon nanotubes, the sensor developed in this study exhibits excellent capability for simultaneous detection of lead and cadmium ions in water. Under optimized conditions, Pb2+ and Cd2+ showed good linear relationships with the peak current in the concentration range of 2.0–50.0 μg/L. In the concentration range studied, the regression equations for Pb2+ and Cd2+ were determined as follows: y = 0.2982x + 0.4553 (r = 0.9962) for Pb2+ and y = 0.3631x + 0.1242 (r = 0.9949) for Cd2+. The detection limits for Pb2+ and Cd2+ were 0.76 μg/L and 0.87 μg/L, respectively. The relative standard deviations (RSDs) for 50 μg/L mixed standard solution of Pb and Cd were 1.89 % and 1.23 %, respectively. Furthermore, the RSDs for the same modified electrode tested with 50 μg/L Pb2+ and Cd2+ mixed standard solution over seven consecutive days were 2.27 % and 1.42 %, respectively, under identical conditions. In practice, the lead and cadmium concentrations of a lake were found to range from 4.42 μg/L to 5.60 μg/L, while the lead and cadmium concentrations of effluent from a wastewater plant ranged from 11.83 μg/L to 14.49 μg/L. This research not only describes a new electrochemical platform for the simultaneous determination of lead and cadmium in water but also provides a new method for the simultaneous determination of lead and cadmium in water. This research is valuable for promoting the application of MOFs in the field of electrochemistry.